Undesirable airborne compounds, including chlorine and sulfur containing compounds, hydrogen sulfide, and oxides of nitrogen, occur in a number of environments, where most primarily are responsible for the presence of disagreeable odors, irritating or toxic gases. Such environments include landfills, petroleum storage areas, oil and gas refineries, water treatment facilities, sewage treatment facilities, hospital morgues, animal rooms, confined livestock operations, swimming pools, and pulp and paper production sites, among others.
There are a wide swath of industries that produce hydrogen sulfide gas. The U.S. Environmental Protection Agency (EPA) is considering broadly regulating hydrogen sulfide which has been increasingly linked to a variety of health problems for people living or working near petroleum, confined livestock, paper and landfill operations (Wall Street Journal Dec. 11, 2007). While it has long been recognized that high concentrations of hydrogen sulfide are deadly, there is growing evidence to suggest that hydrogen sulfide may have health effects at low levels. Recent research shows that prolonged exposure to relatively low levels may effect memory, coordination, eyes and breathing. With the recent national housing boom and series of devastating gulf-coast hurricanes, the number of construction and demolition debris sites has risen dramatically. This has caused the levels of hydrogen sulfide to also rise because gypsum, the main ingredient of wallboard, decomposes to produce hydrogen sulfide as a by-product.
Under current federal rules, companies that produce more than 10,000 pounds of hydrogen sulfide must have a plan to avert and respond to accidental releases of the gas. However, the rules do not generally cover prolonged low-level emissions and contact with people living near hydrogen sulfide sources.
A U.S. multi-state surveillance program found that 637 hydrogen sulfide-related incidents occurred from 1993-2001, resulting in 63 public evacuations and injuring 185 people, according to a 2004 Journal Article written by Federal Health Investigators and others.
More than a dozen states have moved to regulate hydrogen sulfide at lower levels, in the absence of federal rules from the EPA. For example, in 2007, the Department of Environmental Protection for the State of Massachusetts discussed a policy directed to solid waste management regulations for the control of odorous gas at Massachusetts landfills. Other states are proposing benchmark standards for interpreting monitoring data. For example, the Maine Center for Disease Control (ME-CDC) established ambient air guidelines for hydrogen sulfide. These guidelines apply to the general public. The Occupational Health and Safety Administration sets exposure standards for site workers. The ME-CDC's ambient air guidelines of 30 parts per billion (ppb) for acute (short term, 30 minute) exposure and 1 ppb for chronic (long-term, greater than 1 year) exposure are not regulatory standards.
While the oil and gas industries and agricultural operations are believed to be some of the largest producers of hydrogen sulfide, construction and demolition dumps are emerging as major areas of concern. Reports produced by the Federal Agency for Toxic Substances and Disease Registry indicate that hundreds of people living near construction and demolition debris dumps in Ohio and Florida likely have fallen ill in the past decade after being exposed to hydrogen sulfide for days and weeks.
Different methods can be used to check for hydrogen sulfide and are selected based on site-specific needs. For example, hydrogen sulfide can be detected and measured with portable or stationary continuous air monitors. Air sampling and subsequent laboratory analysis can also be conducted.
Hydrogen sulfide and other landfill gases can be controlled by installing an active gas management system that pulls out and burns the landfill gas. Also, hydrogen sulfide emissions can be reduced by applying certain cover materials such as soil amended with lime and fine concrete.
Hydrogen sulfide (H2S) is a colorless, heavier-than-air, toxic gas having the characteristic odor of rotten eggs. It occurs both naturally and from industrial processes. Natural sources include crude oil, natural gas, salt marshes, sulfur springs and swamps. Industrial sources include manure handling operations, oil refineries, pulp and paper mills, wastewater treatment plants and solid waste landfills. Controlling emissions of this gas has long been considered desirable. More recently, protecting electronic apparatus from the corrosive fumes of these compounds has become increasingly important. H2S is also flammable.
Chlorine (Cl2) is a greenish-yellow dense gas with a suffocating odor. The compound is used for bleaching fabrics, purifying water, treating iron, and other uses. Control of this powerful irritant is most desirable for the well-being of those who work with it or are otherwise exposed to it. At lower levels, in combination with moisture, chlorine has a corrosive effect on electronic circuitry, stainless steel and the like. Accordingly, protecting electronic apparatus from the corrosive fumes of chlorine and chlorine by-products is desirable.
Sulfur dioxide (SO2) is a colorless gas. It can be oxidized to sulfur trioxide, which in the presence of water vapour is readily transformed to sulphuric acid mist. Health effects caused by exposure to high levels of SO2 include breathing problems, respiratory illness, changes in lung defences, and worsening respiratory and cardiovascular disease. People with asthma, chronic lung or heart disease are the most sensitive. SO2 also damages trees and crops. SO2, along with nitrogen oxides, are the main precursors of acid rain. This contributes to the acidification of lakes and streams, accelerated corrosion of buildings and reduced visibility.
Oxides of nitrogen, including nitrogen dioxide (NO2) nitric oxide (NO), and nitrous oxide (N2O), are compounds with differing characteristics and levels of danger to humans, with nitrous oxide being the least irritating oxide. Nitrogen dioxide, however, is a deadly poison. Control of pollution resulting from any of these oxides is desirable or necessary, depending on the oxide.
Attempts have been made to provide a solid filtration media for removing the undesirable compounds described above. Desired features of such media are a high total adsorption capacity for the targeted compound, high efficiency in removing the compound from an air or gas stream, and a low ignition temperature (non-flammability). For example, U.S. Pat. No. 4,855,276 describes a solid oxidizing system in pellet form composed of carbon, alumina, and other binders suitably impregnated with chemicals (such as sodium bicarbonate) to enhance the capacity for removal of odorous gases. This pellet provides air purification and odor control by both adsorbing and adsorbing odors, and then destroying the collected odors by the pellet's controlled oxidizing action.
Activated carbon will physically adsorb considerable quantities of hydrogen sulfide. See, for example, U.S. Pat. No. 2,967,587. See also French Patent No. 1,443,080, which describes adsorption of hydrogen sulfide directly by activated carbon, which is then regenerated by hot inert gas or superheated steam.
Better removal of sulfur compounds can be accomplished by the catalysis of the oxidation of hydrogen sulfide to sulfur, based on the ability of carbon to oxidize hydrogen sulfide to elemental sulfur in the presence of oxygen. Additionally, it has been found that potassium sulfate can convert hydrogen sulfide into elemental sulfur. Both the above reactions are advantages because they allow for greater storage of contaminants in the solid filtration media because the contaminants are broken down into smaller molecules and consequently take up less space within the solid filtration media. Ammonia may be added to an influent gas stream of hydrogen sulfide and oxygen to provide catalysis. Silicate-impregnated activated carbon is also effective. The residual adsorbate, however, may not be removed by extraction with alkaline solutions. See South African Patent No. 70/4611. Treatment with a 1% solution of NaOH restores the adsorption capacity of activated carbons used for adsorption removal of hydrogen sulfide gas. Boki, Shikoku Igaku Zasshi, 30(c), 121-8 (1974) (Chemical Abstracts, Vol. 81).
See also, for example, French Patent No. 1,388,453, which describes activated carbon granules impregnated with 1% iodine (I2) for this use. South African Patent No. 70/4611 discloses the use of silicate-impregnated activated carbon. Swinarski et al, Chem. Stosowana, Ser. A 9 (3), 287-94 (1965), (Chemical Abstracts, Vol. 64, 1379c), describe the use of activated carbon treated with potassium salts, including potassium hydroxide (KOH) for hydrogen sulfide adsorption. Activated carbon has also been impregnated with a solution of sodium hydroxide (NaOH) and potassium iodide (KI).
Although not confirmed, U.S. Pat. No. 4,072,479 suggests that hydrogen sulfide is oxidized to elemental sulfur in the presence of activated carbon, and that the presence of moisture on the activated carbon is significant. Another method for removing sulfur and other compounds from gas streams utilizes a product known as Purakol K (Lindair, Ljusne, Sweden). This product contains carbon impregnated with NaOH and KI.
Other uses of impregnated carbon include removing water from air (desiccation), see, for example, Soviet Union Patent No. 1,219,122 (activated carbon combined with aluminum oxide; a binder, calcium hydroxide; and lithium bromide); and the removal of acidic contaminants from gas streams, see, for example, U.S. Pat. No. 4,215,096 (activated carbon impregnated with sodium hydroxide and moisture, for the removal of chlorine from gas streams) and U.S. Pat. No. 4,273,751 (activated carbon impregnated with sodium hydroxide and moisture, for the removal of sulfur oxide gases and vapors from gas streams).
Japanese Patent No. 61-178809 teaches water purification by treatment with activated carbon loaded with metallic copper or copper salts. Several patents teach alumina and carbon adsorbents, including U.S. Pat. No. 3,360,134 (alumina hydrate contacted with a carbonaceous solution; used as a decolorizing agent, a reviving agent for precious metal electroplating bath for the removal of constituents from cigarette smoke, and as an adsorbent in pressure or gravity flow percolation beds); U.S. Pat. No. 4,449,208 (powdered carbon, dense alumina, and a binder, for increasing heat capacity of the adsorbent to enhance the operation of adiabatic pressure swing adsorption processes by decreasing the cyclic temperature change in the adsorbent bed during each cycle of the process); U.S. Pat. No. 3,819,532 (ground graphite and finely divided alumina adsorbent, for removing aromatics, heterocyclics, sulfur compounds, and colored materials from lubricating oils); and U.S. Pat. No. 3,842,014 (ground graphite and alumina binder, for adsorbing paraffin). Such art generally teaches a substrate consisting primarily of activated carbon with a relatively small amount of alumina.
Finally, U.S. Pat. No. 7,101,417 teaches a method of reducing a concentration of hydrogen sulfide present in a gaseous discharge comprising contacting the gaseous discharge with an activated carbon/metal oxide filter element constructed and arranged to exhibit a structural failure when saturated with sulfur, thereby producing a product stream having a reduced hydrogen sulfide concentration, and removing the product stream from the activated carbon/metal oxide filter element. U.S. Pat. No. 7,101,417 indicates that one important advantage of the media claimed is that the media is arranged and constructed to exhibit structural failure when saturated with a odorous compound such as hydrogen sulfide.
None of the methods available thus far have effectively addressed neutralization of large quantities of gases while maintaining structural integrity. Accordingly, there remains a need for a composition having an enhanced capacity for toxic or harmful gases, such as hydrogen sulfide removal. Furthermore, there remains a need for a toxic or harmful gases removal composition that can operate effectively and not present health problems to those who use or install the composition.